KR102430755B1 - Electroplating bath containing trivalent chromium and process for depositing chromium - Google Patents

Abstract

The present invention relates to an electroplating bath for depositing chromium comprising at least one trivalent chromium salt, at least one complexing agent, at least one halogen salt and optionally further additives. (electroplating bath). In addition, the present invention relates to a method of depositing chromium on a substrate using the electroplating bath (electroplating bath).

Description

Electroplating bath containing trivalent chromium and chromium deposition process

The present invention relates to an electroplating bath for depositing chromium comprising at least one trivalent chromium salt, at least one complexing agent, at least one halogen salt and optionally further additives. (electroplating bath). In addition, the present invention relates to a method of depositing chromium on a substrate using the electroplating bath (electroplating bath).

Chrome plating in trivalent chrome plating baths has been known for many years, and many documents in the prior art state that plating deposits can be obtained in trivalent chrome baths.

Currently, it is known that a uniform chromium coating body with a thickness of 0.1 to 1 μm can be prepared from a trivalent chrome electrolyte. This thickness (0.1-1㎛) is very suitable for decorative applications.

However, there are many applications where high wear and/or corrosion resistance is required, such as sanitary equipment, chrome plating on exterior parts of automobiles, as well as functional applications such as plating on rods, pistons or landing gear parts. A thick chromium layer is required. The thickness required in this field is 0.1 to 300 μm.

In US 4,804,446, a method for electrodepositing a smooth, cured coating of chromium is described. The bath contains, as a source of chromium, chromium(III) chloride, citric acid to complex chromium and a wetting agent, preferably Triton X 100. In addition, bromide is added to prevent generation of hexavalent chromium at the anode. The pH of the bath is maintained at 4.0 and the temperature at about 35°C. In addition, in order to advance the reaction kinetics (electrolyte) further includes boric acid (boric acid). However, because of the toxicity and dangers of boric acid, it would be desirable to be free of boric acid in the electroplating bath.

In WO 2009/046181, obtained in a trivalent chromium bath containing carboxylic acid and containing a source for divalent sulfur and a source of carbon, nitrogen and oxygen as alloying components Deposits of nanogranular crystalline functional chromium alloys or amorphous functional chromium alloys are disclosed. The deposits contain 0.05-20 wt % sulfur and the electrodeposition bath used to plate these deposits contains a source of divalent sulfur in a concentration range of about 0.0001M to 0.05M.

In US2013/0220819, a method for producing a dense chrome cured coating in a trivalent chrome plating bath is described. The coating has microhardness values from 804KHN to 1067KHN. This property is achieved using a trivalent chromium electrolyte and pulsed plating with a dedicated cycle of waveforms. The use of pulse currents to electrodeposit hard chromium on complex and large surface parts requires significant modifications to the plating equipment. However, it is preferable not to use a pulsed current to deposit the thick chromium layer described above.

There are many publications on the use and effect of pulsed current and pulsed reverse current in trivalent chromium in the field of hardened chromium.

Publication, Pulse and pulse reverse plating—Conceptual, advantages and applications , MS Chandrasekar, Malathy Pushpavanam Central Electrochemical Research Institute, Karaikudi 630006, TN, India Electrochimica Acta 53 (2008) 3313-3322 Pulse technology and reverse in electrodeposition Regarding a review of pulse technology, pulse electrodeposition (PED) of some metals and alloys is reported. There were effects of mass transport, electrical double layer pulse parameters and current distribution on surface roughness and on morphology. The applications, advantages and disadvantages of PC and PRC technologies along with theoretical aspects and mechanisms are discussed.

Publication, Improving hardness and tribological characteristics of nanocrystalline Cr-C films obtained from Cr(III) plating bath using pulsed electrodeposition , Int. In Journal of Refractory Metals and Hard Materials 31 (2012) 281-283, for Cr-C electrodeposits obtained in a trivalent chromium bath, nanocrystal size, composition, hardness, friction The effect of pulsed electrodeposition on the coefficient of friction and wear resistance was investigated. The electrodeposit was found to contain about 9% carbon. Pulsed electrodeposition did not significantly affect the carbon content. At the same time, as the off-time duration increased, the nanocrystals became smaller. The hardness and wear parameters of the electrodeposits were sufficiently improved when using the pulsed current. For example, at t _on = t _0ff = 1 s, the hardness reached a value of ∼1200 ÷ 1300 HV (while approaching 850 ÷ 950 HV in steady-state electrolysis).

Despite some publications on trivalent chromium deposits, it is still dense and uniform, exhibiting corrosion resistance, hardness and abrasion resistance equivalent to deposits produced from Cr0 ₃ based electrolytes of 0.1 to 300 μm. There is a need for a commercial system capable of plating thick chromium deposits of consistent thickness.

The present invention therefore seeks to provide an electroplating bath that provides a chromium layer having a dense and uniform structure of thickness forming a layer that can be used for high wear and/or corrosion resistance. The purpose.

This object is solved by an electroplating bath having the features of claim 1 and a method of depositing a chromium layer having the features of claim 13 .

According to the present invention, there is provided an electroplating bath for depositing chromium comprising:

a) from 100 to 400 g/L of at least one trivalent chrome salt,

b) from 100 to 400 g/L of at least one complexing agent,

c) from 1 to 50 g/L of at least one halogen salt and

d) 0 to 10 g/L of additives.

In addition, the pH of the electroplating bath is 4 to 7. In the present invention, it is essential that the electroplating bath is substantially free of divalent sulphur compounds and boric acid and/or borates and derivatives.

It has surprisingly been found that an innovative electroplating bath can provide a layer with a dense and uniform structure. Since a layer with a thickness of 10 to 400 μm is provided, it is possible to use the layer in the field of high wear and/or corrosion resistance.

The trivalent chromium salt is preferably chromium (III) sulfate in acidic form or chromium (III) sulfate in alkaline form, chromium (III) chloride, chromium (III) chromium(III) acetate, chromium(III) hydroxyacetate, chromium(III) formate, chromium(III) hydroxyformate ) hydroxyformate), chromium (III) carbonate, chromium (III) methanesulfonate, potassium chromium (III) sulfate (potassium chromium (III) sulphate) and mixtures thereof selected from the group consisting of

The trivalent chromium salt is preferably present in an amount of 100 to 400 g/L, particularly 120 to 160 g/L.

A major disadvantage associated with the electrolytes described in the prior art relates to the accumulation of counterions of trivalent chromium salts. In particular, very much Cr(III) in such a bath can be consumed when the target thickness is in the upper range of >10 μm. Counterions associated with trivalent chromium cations will then accumulate in the electrolyte, resulting in some disadvantages such as increased bath density and risk of precipitation. The dry content of the bath will increase to the point where the trivalent chromium salt can no longer be dissolved due to solubility limit.

Thus, one embodiment of the present invention includes "temporary" anions that can be consumed electrolytically that will not accumulate in the electrolyte to the same extent as "permanent" anions (such as sulfate). It is to select the counter ion of the trivalent chromium salt. Among these transient anions, formate, acetate, propionate, glycolate, oxalate, carbonate, citrate and combinations thereof are preferred.

Innovative electroplating baths are preferably selected from the group consisting of vanadium, manganese, iron, cobalt, nickel, molybdenum, tungsten and indium. selected alloy formers. The organic components of the bath and ammonia are sources for carbon, nitrogen and oxygen taken up by the alloy during deposition. Urea as an additive is particularly effective. Preferably, the electroplating bath comprises ammonia in a molar concentration, in particular below the molar concentration of the at least one complexing agent. More preferably, the concentration of ammonia is between 70 g/L and 110 g/L.

Alloys, such as aluminum and/or gallium, because they form mixed-metal complexes with chromium(III) in the bath, which affects the kinetics and mechanism of deposition. It is advantageous if there are metal salts that are not codeposited together. However, the electroplating bath may be free of such metal salts (eg aluminum salts).

According to the present invention, the complexing agent is preferably carboxylic acid and a carboxylate salt, preferably formic acid, acetic acid, propionic acid, glycolic acid ), lactic acid, oxalic acid, malic acid, citric acid, tartaric acid, succinic acid, gluconic acid, glycine, aspartic acid, glutamic acid, and mixtures thereof, or salts thereof and mixtures of salts thereof.

The complexing agent is preferably present in an amount of 100 to 300 g/L, more preferably in an amount of 150 to 250 g/L. The molar ratio of complexing agent to trivalent chromium salt is from 8:1 to 15:1, preferably 10: 1 to 13:1.

A halogen salt present in the electroplating bath acts as a suppressor in the generation of hexavalent chromium in the bath. The halogen salt is preferably selected from the group consisting of bromide salts, chloride salts, iodide salts, fluoride salts and mixtures thereof. A bromide salt is more preferable, and in particular, potassium bromide, sodium bromide, ammonium bromide and mixtures thereof are preferable. The halogen salt is preferably present in an amount of 5 to 50 g/L.

Additives to the electroplating bath include brighteners such as polyamines or mixtures of polyamines containing quaternary ammonium compounds (preferably brightening agents such as those recited in US 7964083 patent) and It is selected from the group consisting of a wetting agent such as an electronic surfactant, a cationic surfactant, and an amphoteric surfactant.

Particularly preferably, the electroplating bath is (substantially) free of chloride ions and/or (substantially) free of ammonium ions, but the bath is free of at least one further complexing agent ( as a ligand) and/or as at least one other halogen salt - fluoride, which aids in ligand exchange of the chromium(III) complex in the bath.

According to the present invention, there is provided a method for depositing chromium on a substrate comprising the steps of:

- providing the above-described electroplating bath;

- immersing the substrate in the electroplating bath, and

- applying an electric current to deposit chromium on the substrate.

The temperature during deposition is preferably 20 to 60°C, more preferably 30 to 50°C.

The electroplating bath can be separated from the anode by a membrane, preferably by an anionic exchange membrane, a cationic exchange membrane or a porous membrane, more preferably by a cation exchange membrane. have. The cation exchange membrane has the advantage of preventing the migration of sulfate in the catholyte.

The anode used to perform the deposition may be formed of an insoluble material such as graphite or mixed oxides materials such as titanium covered with oxides of tantalum and iridium.

In one embodiment of the present invention, in order to prevent certain components of the electroplating bath from contacting the anode and to trap unwanted oxidation breakdown products, the anode comprises an anolyte and a cathode It may be surrounded by a suitable material, defined as catholyte.

For example, types of unwanted products are oxidation products of complexing agents at the anode as well as Cr(VI) resulting from the anodization of Cr(III).

Another advantage of using a barrier material to separate the anode region from the bath is that it avoids the deposition of product types such as sulfates, such as replenishment of chromium(III) sulfate, which are deposited in the catholyte without being electrodeposited. is to prevent

The barrier may be a material selected from the type of the ion exchange membrane. The barrier may be a cation exchange membrane such as Sybron IONAC material MA 3470 or the like. In addition, an anion exchange membrane such as a Nafion membrane (manufactured by Du Pont) may be used. A preferred anion exchange membrane is an N424 membrane. In addition, porous membranes, such as those described in EP 1 702 090, can also be considered as suitable materials for defining an anodic compartment separated from the rest of the electrolyte.

The anodic compartment may be filled with any conducting substance compatible with the electrolyte. The anode compartment may be acidic or alkaline. Because of the slightly acidic pH of the parent catholyte, an acidic pH will be preferred for the anolyte. Formic acid, acetic acid, propionic acid, glycolic acid, citric acid, as well as mineral acids such as H ₂ S0 ₄ and H ₃ P0 ₄ are employed can be Chromium(III) sulfate solution may also be used as an anolyte. Alternatively, sodium hydroxide, potassium hydroxide, lithium hydroxide or any kind of alkaline solution without CMR properties may be used as the anolyte in the method of the present invention.

The current applied to the electrolyte may be a direct current or a pulsed current. The use of a pulsed current sequence provides the ability to plate deposits that are less susceptible to crack formation due to hydrogen accumulation at the interface.

The pulse sequence may consist of a cathodic phase followed by T off to help remove hydrogen from the interface, or eventually the anodic phase will oxidize hydrogen at the interface. can be used.

The present invention will be further illustrated by the following drawings and examples. However, the present invention is not limited to these specific embodiments.
1 shows a schematic diagram of an anodic setup according to an embodiment of the present invention.
2 shows a graph showing the development of sulfate concentration in different electroplating systems.

Example 1 shown in FIG. 1 uses an anolyte 7 that can serve as a reservoir for Cr(III) ions. A solution of a trivalent chromium salt such as chromium sulfate or a solution of another chromium salt comprising 10-50 g/L of trivalent chromium and 30-140 g/L of sulfate anions or other anions is shown in FIG. used as a component of the anolyte (7). An ion exchange membrane 3 may be included or an ion exchange membrane may be coupled to a carrier 2 and preferably the ion exchange membrane will be selected as a cation exchange membrane such as Nafion N424 described above. The catholyte 5 is made of the trivalent chrome electrolyte of the present invention as described in Example 2 below. The anode 6 is formed of a graphite material. A part of the sample to be plated is placed as the cathode 4 . The anolyte is supplemented with a chromium salt in the form of chromium(III) sulfate.

In Figure 2, the graph demonstrates the time-dependence of sulfate concentration in different electroplating systems. In an electroplating system based on a bath with membraneless Cr(III) sulfate, while the sulfate concentration increases rapidly, the concentration and membrane separation in the first embodiment according to the invention using a “temporary” anion The concentration in the second embodiment according to the invention used is kept substantially constant during the measurement time.

Table 1 shows the composition of the electroplating bath of Examples 1-4 of the present invention and the composition of Comparative Example based on Cr(VI) and operating parameters in each electroplating bath.

comparative example Example 1 Example 2 Example 3 Example 4 CrO ₃ 300g/L H ₂ SO ₄ 3.5g/L organic catalyst 50mL/L Chromium Sulfate Base 140g/L
(0.46M) 140g/L
(0.46M) 140g/L
(0.46M) 140g/L
(0.46M) formic acid 250g/L
(5.43M) 250g/L
(5.43M) 250g/L
(5.43M) 250g/L
(5.43M) NH ₃ 90g/L
(5.3M) 90g/L
(5.3M) 90g/L
(5.3M) 90g/L
(5.3M) KBr 10g/L
(0.085M) 10g/L
(0.085M) 10g/L
(0.085M) 10g/L
(0.085M) PEG400 0.5 g/L 0.5 g/L 0.5 g/L 0.5 g/L quaternary ammonium compound 1 g/L 1 g/L 1 g/L 1 g/L operating parameters temperature 50℃ 35~45℃ 35~45℃ 35~45℃ 35~45℃ current density 50A/dm2
DC 50A/dm2
DC 50A/dm2
PRC pH - 5-5.5 5-5.5 5-5.5 5-5.5 negative duty cycle 96% 96% 96% frequency 6.5Hz 6.5Hz 6.5Hz magnetic induction 300℃-2 seconds 300℃-2 seconds

DC : Direct current

PRC: Pulse Reverse Current

Table 2 shows the properties of the deposits obtained in the electroplating bath of Table 1.

comparative example Example 1 Example 2 Example 3 Example 4 Thickness (㎛) 130㎛ 130㎛ 130㎛ 130㎛ 130㎛ Hardness (HV) 1000-1200 750-800 800-900 1100-1200 1900-2100 Adhesion according to Chiselling UNI EN ISO 2819 excellent poor good excellent excellent Cathode Efficiency
(cathodic efficiency) 25-30% 12-15% in Cr(III) 12-15% in Cr(III) 12-15% in Cr(III) 12-15% in Cr(III) crystallinity decision amorphous amorphous decision decision Chemical composition (by XPS) Cr>99 Cr=92.5-95%w
C=2-3%w
O=3-4%w
N=0.1-0.5%w Cr=92.5-95%w
C=2-3%w
O=3-4%w
N=0.1-0.5%w Cr=92.5-95%w
C=2-3%w
O=3-4%w
N=0.1-0.5%w Cr=92.5-95%w
C=2-3%w
O=3-4%w
N=0.1-0.5%w

Claims (15)

An electroplating bath for depositing chromium or a chromium alloy, comprising:
a) from 100 to 400 g/L of at least one trivalent chromium salt,
b) from 100 to 400 g/L of at least one complexing agent and
c) from 1 to 50 g/L of at least one halogen salt,
The electroplating bath has a pH of 4 to 7, and substantially does not contain divalent sulphur compounds and boric acid, borates and/or derivatives,
The molar ratio of the complexing agent to the trivalent chromium salt is 8:1 to 15:1,
The electroplating bath further comprises carbon, oxygen and nitrogen provided from an organic component of the electroplating bath or ammonia. According to claim 1,
The trivalent chromium salt is chromium (III) sulfate in an acidic form or chromium (III) sulfate in an alkaline form, chromium (III) chloride, chromium (III) acetate (chromium (III) acetate), chromium (III) hydroxyacetate, chromium (III) formate, chromium (III) hydroxyformate, chromium (III) hydroxyformate III) carbonate (chromium (III) carbonate), chromium (III) methanesulfonate (chromium (III) methanesulfonate), potassium chromium (III) sulfate (potassium chromium (III) sulphate) and mixtures thereof, electroplating bath. 3. The method of claim 1 or 2,
The trivalent chromium salt is present in an amount of 120 to 160 g / L, electroplating bath. 3. The method of claim 1 or 2,
The anion of the trivalent chromium salt is an anion of a volatile acid or an electro-chemically consumable acid. 3. The method of claim 1 or 2,
The electroplating bath is an alloy forming body selected from the group consisting of vanadium, manganese, iron, cobalt, nickel, molybdenum, tungsten, and mixtures thereof. (alloy former), including an electroplating bath. 3. The method of claim 1 or 2,
The complexing agent is selected from the group consisting of carboxylic acids and carboxylate salts, and mixtures thereof. 3. The method of claim 1 or 2,
The complexing agent is present in an amount of 100 to 300 g/L, and/or the molar ratio of the complexing agent to the trivalent chromium salt is from 10:1 to 13:1. 3. The method of claim 1 or 2,
The halogen salt is selected from the group consisting of a bromide salt, a chloride salt, an iodide salt, a fluoride salt, and mixtures thereof, and/or the halogen The salt is present in an amount of 5 to 50 g/L, the electroplating bath. 3. The method of claim 1 or 2,
The electroplating bath further comprises fluoride as at least one further complexing agent and/or at least one further halogen salt. 3. The method of claim 1 or 2,
wherein the electroplating bath is substantially free of chloride ions and/or substantially free of ammonium ions. - providing the electroplating bath of claim 1 or 2;
- immersing the substrate in the electroplating bath; and
- a method of depositing chromium on a substrate comprising applying an electric current to deposit trivalent chromium on said substrate. 12. The method of claim 11,
wherein the electroplating bath is separated from the anode by a membrane defining an anolyte and a catholyte. 13. The method of claim 12,
The method of depositing chromium on a substrate wherein the anolyte comprises chromium (III) sulphate. delete delete

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